BMT

Paints and Varnishes

1. Introduction

Paints and varnishes are surface finishing materials used in building construction to enhance aesthetic appeal, provide protection against environmental effects, and improve durability. These materials form a thin film over surfaces to prevent deterioration due to moisture, sunlight, temperature variation, chemical attack, and mechanical wear.

2. Paints

2.1 Definition

A paint is a pigmented liquid or semi-liquid material that, when applied to a surface in a thin layer, forms an opaque solid film upon drying. It is used to protect or decorate substrates such as masonry, wood, steel, or plastered surfaces.

2.2 Constituents of Paint

Constituent	Function	Examples
Base	Provides body, strength, and protection	White lead, zinc oxide, red lead
Vehicle (Binder)	Holds pigment in suspension and forms film	Linseed oil, alkyd resin, epoxy resin
Pigment	Provides color, opacity, and protection from UV rays	Titanium dioxide, iron oxide, zinc chromate
Solvent (Thinner)	Adjusts viscosity and aids in application	Turpentine, mineral spirits
Drier (Catalyst)	Accelerates drying by oxidation	Lead acetate, cobalt naphthenate
Additives	Improve specific properties (fungicide, anti-settling agents)	Silicone additives, plasticizers

2.3 Types of Paints

Type	Base Material / Binder	Characteristics	Common Uses
Oil Paint	Linseed oil	Durable, glossy, slow-drying	Wood, metal, plaster
Water-based / Emulsion Paint	Acrylic or vinyl emulsions	Fast drying, low odor, washable	Interior/exterior walls
Cement Paint	White cement base	Waterproof, breathable	External masonry surfaces
Enamel Paint	Alkyd resin	Glossy, chemical-resistant	Metal, wood, furniture
Epoxy Paint	Epoxy resin + hardener	Chemical & abrasion resistant	Industrial floors, tanks
Polyurethane (PU) Paint	Polyurethane resin	High gloss, UV stable	Exterior metallic surfaces
Aluminium Paint	Aluminium flakes in varnish	Reflective, corrosion-resistant	Roofs, pipelines, storage tanks
Bituminous Paint	Bitumen dissolved in mineral spirit	Water-resistant, black finish	Underwater structures, pipes
Heat Resistant Paint	Silicone resin + metal oxides	Withstands high temperatures	Boilers, chimneys

2.4 Properties and Requirements of Good Paint

A good paint should have:

• High covering power and opacity
• Uniform color and gloss
• Resistance to weather, water, and alkalis
• Good adhesion to substrate
• Ease of application and drying
• Non-toxic and environmentally safe composition

2.5 Functions of Paint in Construction

• Protective: Prevents corrosion, rust, and decay.
• Decorative: Enhances appearance and aesthetics.
• Hygienic: Prevents mold, fungus, and bacterial growth in interiors.
• Functional: Provides reflectivity, insulation, or anti-slip surfaces.

2.6 Application of Paints

Surface Preparation:

1. Clean surface — remove dust, oil, grease, and rust.
2. Apply primer coat for adhesion.
3. Apply undercoat for smoothness.
4. Finish with one or two top coats of paint.

Methods of Application:

• Brush painting – common and economical.
• Roller painting – for large wall areas.
• Spray painting – uniform coating, used for steel or concrete structures.
• Dip coating / Flow coating – industrial mass production.

3. Varnishes

3.1 Definition

A varnish is a transparent or translucent solution of resin in a drying oil or volatile solvent. When applied to a surface, it forms a hard, glossy, and protective film without hiding the surface texture or color.

3.2 Constituents of Varnish

Constituent	Function	Examples
Resin	Provides body and gloss	Copal, amber, shellac, synthetic resin
Drying Oil	Acts as vehicle and forms film	Linseed oil, tung oil
Solvent	Reduces viscosity for application	Turpentine, alcohol
Drier	Accelerates oxidation and drying	Lead acetate, cobalt naphthenate

3.3 Types of Varnish

Type	Base	Properties	Applications
Oil Varnish	Natural resin + drying oil	Flexible, durable, slow drying	Interior woodwork
Spirit Varnish	Resin dissolved in alcohol	Quick drying, less durable	Furniture, musical instruments
Turpentine Varnish	Soft resin + turpentine	Inexpensive, moderate quality	Temporary coatings
Asphalt Varnish	Asphalt in turpentine	Dark, waterproof, protective	Metal and concrete surfaces
Synthetic Varnish	Synthetic resins (PU, epoxy)	Highly durable, UV stable	Exterior wood, steel, floors

3.4 Properties of a Good Varnish

• Should dry quickly and form a hard, uniform film
• Must be transparent and glossy
• Provide protection against moisture, UV radiation, and abrasion
• Should not crack or peel over time

3.5 Application of Varnish

1. Surface Preparation: Smooth, dry, and dust-free surface.
2. Application: Apply thin coats using a brush or spray.
3. Drying: Allow each coat to dry fully before applying the next.
4. Polishing: Optional — for additional sheen and smoothness.

4. Selection of Suitable Paint or Varnish in Building Construction

Surface Type	Recommended Paint/Varnish	Key Considerations
Exterior masonry	Cement-based or emulsion paint	Weather resistance, breathability
Interior walls	Acrylic emulsion paint	Washable, non-toxic
Metal surfaces	Enamel or epoxy paint	Rust prevention, hardness
Wooden doors/furniture	PU or spirit varnish	Gloss, scratch resistance
Industrial floors	Epoxy/PU coating	Chemical & abrasion resistance

5. Testing and Quality Control

Property	Standard Test (IS Code)	Remarks
Consistency & viscosity	IS 101 (Part 1/Sec 5)	Ensures uniform application
Drying time	IS 101 (Part 3/Sec 1)	Assesses curing performance
Adhesion	IS 101 (Part 5/Sec 3)	Determines bonding strength
Resistance to water/alkali	IS 101 (Part 6/Sec 1)	Evaluates durability
Gloss and color	IS 2932	Ensures appearance conformity

6. Advantages and Limitations

Advantages:

• Enhances durability and aesthetics.
• Protects against corrosion, dampness, and UV light.
• Easy maintenance and cleaning.

Limitations:

• Periodic repainting required.
• VOC emissions may affect indoor air quality.
• Surface defects (blistering, flaking) possible with poor application.

7. IS Codes and References

Code	Title
IS 2932	Specification for enamel paints
IS 428	Distemper, dry colour type
IS 101	Methods of sampling and testing paints, varnishes and related products
IS 110	Ready mixed paint, brushing, bituminous, black
IS 133	Ready mixed paint, brushing, oil, for general purposes
IS 15489	Polyurethane paint specification

8. Summary

Paints and varnishes are essential for protection, preservation, and decoration of construction materials. Their selection depends on substrate, exposure conditions, and functional requirements. Proper surface preparation, correct application method, and adherence to BIS standards ensure long-term performance and aesthetics.

9. Review Questions

1. Define paint and varnish. Differentiate between them.
2. What are the main constituents of paint?
3. Discuss types and applications of varnishes.
4. Explain the importance of surface preparation before painting.
5. Write short notes on: (a) Epoxy paint (b) Cement paint (c) PU varnish